Feature: Add Comprehensive Java Examples

[basukinath]

This pull request significantly expands the project by adding a wide range of examples covering core Java concepts and modern features. The new code is organized into dedicated packages for clarity and ease of navigation.

Key Additions:

• Collections Framework: Added examples for List, Set, Map, Queue, Iterator, Comparable, and Comparator.
• Exception Handling: Included examples for try-catch-finally, checked vs. unchecked exceptions, and custom exceptions. Also fixed a resource leak in the CheckedVsUncheckedException example.
• Java I/O: Provided examples for file handling and object serialization/deserialization.
• Multi-threading and Concurrency: Added comprehensive examples covering Thread, Runnable, synchronization, the Executor framework, and various concurrency utilities.
• Generics: Included examples for generic classes, methods, wildcards, and type erasure.
• Java 8+ Features: Added examples for modern Java features like Lambda expressions, Streams API, Optional, the new Date/Time API, and default methods in interfaces.

These additions make the repository a more robust learning resource for Java programming.